The present invention relates generally to a semiconductor device which acts as a differential light detector.
Fiber obtical sensors, where the light intensity (or polarization which can be converted into an intensity change) is changed by the environment of the fibers (e.g., pressure, curvature, temperature) are usually operated with a reference beam from the same source in order to compensate for fluctuations or degradation of the input light. The proposed device facilitates this comparison. Novel optical A/D converters and other applications of integrated optical signal processing makes use of Mach-Zehner interferometers which decrease the light transmitted according to an impressed electronic signal. The transmitted light intensity is subsequently compared with a reference intensity which bypassed the interferometer. The proposed device is ideally suited to make this comparison more accurately and at higher speeds than presently used methods.
U.S. patents of interest include U.S. Pat. No. 3,531,645 to Marie DeJong, which shows in FIG. 2 a pair of photoresistors connected in a bridge circuit so as to give a differential output. The bridge circuit is described in the patent as useful for comparing two light intensities. U.S. Pat. No. 4,179,702 to Lamorte is directed to a monolithic cascade solar cell used in converting incident light radiation into electrical energy. This patent shows in FIG. 4 a three-terminal device with a voltage opposing configuration. A circuit with two PIN photodiodes is shown in Fang et al U.S. Pat. No. 4,447,746. In Benjamin et al U.S. Pat. No. 4,533,783 a solar cell provices alternating current. Light-generated hole-electron pairs alternately diffuse in opposite directions across alternately induced PIN junctions. U.S. Pat. No. 4,600,935 to Dresner discloses back-to-back diodes and U.S. Pat. No, 4,582,952 to McNeely is concerned with a gallium arsenide type solar cell.